Miniature electrolytic timer with an erodable anode



Sept. 7, 1965 R. J. LYON MINIATURE ELECTROLYTIC TIMER WITH AN ERODABLE ANODE Filed Jan. 21, 1964 FIG. 3

Rober! J. Lyon INVENTOR.

BY i s i ATTORNEY.

MLJLLL'IA AGENT United States Patent Office 3,205,321 Patented Sept. 7, 1965 The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to the art of time delay mechanisms. More particularly, the invention relates to an electrolytic interval timer in which a spring biased plunger is restrained by means of an electrolytically erodable anode element which after being eroded for a predetermined period of time will release the plunger to allow it to move forward under the action of the spring. The motion of the plunger may then be utilized in any desired manner as, for example, to actuate an electric switch.

, Previous electrolytic timers of the nature of the present device have had the disadvantage of being relatively heavy and large. As such, they have not been suitable for use in missile, mines, satellites and like applications where space and weight are important. Moreover, previous timers have not been suiiiciently reliable in operation for various reasons. For example, some used lead electrodes and lead base electrolytes which produced a highly conductive sludge during the deplating operation, with the consequent danger of shorting the anode to the cathode.

It is therefore an object of the invention to provide an electrolytic timer which is smaller and lighter in weight than previous timers so as to be useful where space and weight are important, such as in missiles and satellites.

It is a further object of the invention to provide an electrolytic timer which is reliable and accurate in operation. Acceptable accuracy for an interval of as much as several weeks is about $15 The objects of the invention are achieved by the present device in part by details of construction which result in small size and light weight. A clean electrolyte is maintained by a selection of electrode materials and electrolyte which do not produce sludge. The particular electrolyte selected provides a further advantage in that the subject timer is operative at as low a temperature as 10 F.

In general, the timer of this invention consists of an electrolytic cell for controlling a spring biased plunger between a retracted position and an advanced position, the motion of the plunger from the iirst to the second position actuating an electric switch. The plunger is restrained in the retracted position by an enlarged head portion of an anode element which extends into a chamber containing an electrolyte. When an electric current is passed through the electrolyte, erosion of the anode takes place, and depending on the size of the anode and the magnitude of the current, operation may be delayed for a predetermined time, after which the restraint provided by the anode will be removed to permit the plunger to move forward to the extended position.

Other objects and advantages of the invention will become apparent from a consideration of the following detailed description when read in conjunction with the accompanying drawings, wherein:

FIG. 1 is a longitudinal cross-section through one embodiment of the invention;

FIG. 2 is an end view of an electrical switch that may be employed with the subject timer and,

FIG. 3 is a view, similar to FIG. 1, of another embodiment of the invention.

Referring now to FIG. 1, the electrolytic cell of the invention is there seen to consist of a plastic cell housing 1t) defining an electrolyte chamber 11 therein. Cell housing 10 is formed with an outer cylindrical wall 12, and a transverse end Wall 13 near one end thereof. The end of the casing opposite wall 13 is closed by a plunger housing 14 which consists of a cylinder 15 of smaller outer diameter than the inner diameter of wall 12 and a conical end portion 16. Plunger housing 14 is provided with a coaxial central bore 17, which opens through the apex end of portion 16, and with counterbores 18, 19 and 2G, which serve to support various elements as will appear hereinafter, although the term counterbores is not meant to include only a machined structure. The designated shape can clearly be produced by molding as well as machining.

In the FIG. 1 embodiment, plunger housing 14 is integrally formed with outer wall 12 being joined thereto as indicated at 22.

In order to facilitate the manufacture of the device, transverse wall 13 may be made in this embodiment as a separate element and heat sealed in housing 10 after plunger housing 14 is fabricated.

In the FIG. 3 embodiment, the plunger housing is a separate element as will appear in more detail hereinafter. In this embodiment transverse wall 13 may if desired be integrally molded with housing 1t).

The anode and plunger assembly, generally indicated at 23, is the same for both embodiments and will be described in detail only with respect to FIG. 1. The plunger 24 itself consists of a head 25 and a tubular tail 26. Head 25 has a bore 27 coaxial with tail 26 and a slot 28 intersecting the bore 27 and of at least the same width as the diameter of bore 27. The anode is an elongated wire 29 which passes through bore 17 and terminates in an enlarged head portion 31 within electrolyte chamber 11. An O-ring 32 is disposed in counterbore 19 to provide a fluid seal between the anode wire 29 and plunger housing 14.

The distance from O-ring 32 to the apex of portion 16 is chosen so as to be greater than the maximum distance of travel of the plunger. With this construction, the anode wire 29 cannot be pulled out of the O-ring 32 and the seal is maintained both before and after operation of the timer and no leakage of electrolyte out of the chamber can take place. A washer 33 rests against the step between counterbores 19 and 20, serving to hold O-ring 32 in place and also serving to provide a support for the innner end of biasing spring 34 which acts between washer 33 and the rear end 36 of the head 25 of plunger 24.

yIn assembling the plunger assembly, anode Wire 29 is first passed through bore =17 'from the inside of the chamber. O-ring 32, washer 33 and spring 34 are then dropped into place in proper order. Plunger 24 is then slid over anode wire 29 and pressed in, compressing spring 34, until wire 29 protrudes out into slot 28. Wire 29 is 3 then bent over as shown in order to secure the plunger in the retracted position.

Connected in any suitable manner to the left end of cell housing is a switch element 40 having a transverse mounting plate 41, made of an insulating material, with an aperture 42 centrally disposed therein to accommodate the `forward end of plunger `24. Attached to plate 41 in any suitable manner, as by rivets 43, are a stationary contact 44 and `a movable contact 45 -fabricated of sheet lmetal. In the illustrative embodiment shown, it is clear .that the 'switch is arranged to be normally open and to be closed when forward motion of `the plunger 24 moves contact 4S into engagement 'with contact 44. It should be apparent, however, that the parts may be arranged so that the switch is moved from closed to open position, or other switch arrangements may be employed if desired.

Electrical connection is made to the anode by means of a connector 50 which extends through an opening 51 in plate 41. At the Iinner end, connector 50 is bent into a generally hooklike shape as shown at 52. Connector 50 is at -least slightly resilient so that the free end 53 will be biased against the end of anode wire 29 when the switch element 40 is connected to the cell hou-sing 10. A lead 54 extends to suitable control circuitry, not shown.

Completing the electrolytic cell is the cathode element 66 which extends through and is secured in wall 13 in any suitable manner `as by a threaded connection 62. Cathode element 60 has a terminal 63 thereon to which a lead -64 `from the above-mentioned control circuitry may be attached. The opening in which the cathode is secured may also serve as the filling opening through which the electrolyte may be introduced into -chamber 11. The insertion of cathode element 60 then closes and seals the chamber. It should be here noted that it is desirable not to completely iill the chamber with electrolyte so as to leave an air bubble 65 in the chamber to allow for expansion and contraction of the electrolyte during temperature changes. lIt is contemplated that the present timer may be used in areas where the temperature may at times get low enough to freeze the electrolyte and the presence of the air bubble insures that the casing will not be ruptured if this occurs. It is also noteworthy that the construction of the plunger housing to place the `anode head 31 at the end of `'conical section 116 serves to insure that bubble 65 will not surround head 31 in the event that the timer should find itself in a position in `which the `anode i-s uppermost in the casing. The device would obviously be inoperative if the anode were not -completely immersed in the electrolyte.

As stated above, in the FIG. 3 embodiment, the plunger housing, designated 14, is a separate and distinct element although it is formed with the same configuration as described above. In this embodiment, the cylindrical wall of the cell is designated 70 and the transverse end wall 71. .The cathode 72 is here molded into end wall 71, lling of the electrolyte lchamber being possible from the other end of fthe chamber.

Near the end yof the chamber opposite wall 71, cylindrical wal-l 70 is formed with an internal annular flange 73. Plunger housing l14 has an yannular flange 74 thereon which cooperates with flange 73 to define the inserted position of housing 14. A gasket 7S is employed to provide a `iiuid seal between the parts. Housing 14 is held in place by means of a retaining ring 76 disposed in a suitable groove in wall '70.

As pointed out above, the plunger assembly 23 is the same in the FIG. 3 embodiment yas in FIG. 1. This is true also of the switch assembly 40, so that nothing more need be said about the construction of the FIG. 3 embodiment.

In order to avoid the problems of sludge formation and thereby increasing reliability, the anode and cathode have been made of silver, and the electrolyte is silver uoborate, which has been found to be a satisfactory combination of materials. The silver iiuoborate electrolyte provides the added advantage of allowing operation of the device at as low a temperature as -10 F.

ln the operation of both described embodiments, the size of anode head I31 and the current to be passed through the electrolyte are first .predetermined in order to establish the delay time. When it is desired to start the device, the control circuit is closed to supply the predetermined current to the cell. Electrolytic erosion of the silver anode head 31 then takes place until the size of the head is reduced far enough to remove the restraint on the spring biased plunger. At that time, the plunger moves forward to actuate switch 40, and the cycle is complete.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope yolf the appended claims the invention may be practiced otherwise than as speciically described.

I claim:

1. An electrolytic time delay device comprising:

a cell having an electrolyte chamber therewithin,

a cathode element at one side of said cell and extending into said chamber,

a plunger housing at the other side of said cell, said plunger housing having an opening therein extending into said cell,

an anode element in said opening and having an enlarged head portion larger than said opening disposed within said chamber,

a plunger attached to said anode element,

a spring acting between said plunger housing and said plunger for urging said plunger away from said chamber until said head portion engages the wall of said chamber, thereby delining a retracted position for said plunger, and

an electrolyte in said chamber,

whereby when an electric current is established in said electrolyte, said enlarged head portion on said anode is eroded until it is small enough to pass through said opening whereupon said plunger is moved forward by said spring to an advanced position.

2. A device as recited in claim 1, wherein said plunger housing and said cell are each of plastic material and are molded as a single piece.

3. A device as recited in claim 2, wherein both said anode and said cathode are made of silver, and said electrolyte is silver fluoborate.

4. A device as recited in claim 1, wherein said plunger housing and said cell are each of plastic material and are formed as separate elements,

said cell having an aperture therein,

said plunger housing having a portion extending through said aperture and a flange for cooperation with the wall of said cell around said aperture,

a gasket between said flange and said wall of said cell,

and

retaining means for holding said plunger housing in place in said aperture.

5. A device as recited in claim 4, wherein both said anode and said cathode are made of silver, and said electrolyte is silver liuoborate.

6. An electrolytic time delay device comprising,

a cell housing formed ofy plastic material and having an electrolyte chamber therewithin, said cell housing further having a cylindrical wall and a transverse Wall near one end thereof, said transverse wall having a silver cathode extending therethrough,

a plastic plunger housing closing the end of said cell housing, said plunger housing comprising a cylinder of smaller outside diameter than the inner diameter of said cylindrical wall extending into said chamber and having a conical end portion thereon, and a coaxial central bore in said plunger housing which opens through the apex of said conical end portion,

a silver anode in said bore, said anode having an enlarged head thereon disposed within said chamber,

5 larger in transverse extent than the diameter of said bore,

a plunger attached to said anode,

a spring acting between said plunger and said plunger housing for urging said plunger outward of said plunger housing, outward motion of said plunger being limited by engagement of said enlarged head with the apex of said conical portion, and

a silver uoborate electrolyte in said chamber, said chamber being incompletely illed with electrolyte so as to leave an air bubble, therein,

whereby when an electric current is passed through said electrolyte, said enlarged head on said anode is eroded until it is small enough to pass through said 6 bore, whereupon said plunger is moved forward by said spring.

7. A device as recited in claim 6 wherein a switch element is attached to said cell in position to be actuated by the forward movement of said plunger.

8, A device as recited in claim 6 wherein said cell housing and said plunger housing are molded as a single element.

References Cited by the Examiner UNITED STATES PATENTS 2,741,182 4/56 Faust et al.

BERNARD A. GILHEANY, Primary Examiner. 

1. AN ELECTROLYTIC TIME DELAY DEVICE COMPRISING: A CELL HAVINGAN ELECTROLYTE CHAMBER THEREWITHIN, A CATHODE ELEMENT AT ONE SIDE OF SAID CELL AND EXTENDING INTO SAID CHAMBER, A PLUNGER HOUSING AT THE OTHER SIDE OF SAID CELL, SAID PLUNGER HOUSING HAVINGAN OPENING THEREIN EXTENDING INTO SAID CELL, AN ANODE ELEMENT IN SAID OPENING AND HAVING AN ENLARGED HEAD PORTION LARGER THAN SAID OPENING DISPOSED WITHIN SAID CHAMBER, A PLUNGER ATTACHED TO SAID ANODE ELEMENT, A SPRING ACTING BETWEEN SAID PLUNGER HOUSING AND SAID PLUNGER FOR URGING SAID PLUNGER AWAY FROM SAID CHAMBER UNTIL SAID HEAD PORTION ENGAGES THE WALL OF SAID CHAMBER, THEREBY DEFINING A RETRACTED POSITION FOR SAID PLUNGER, AND AN ELECTROLYTE IN SAID CHAMBER, WHEREBY WHEN AN ELECTRIC CURRENT IS ESTABLISHED IN SAID ELECTROLYTE, SAID ENLARGED HEAD PORTION ON SAID ANODE IS ERODED UNTIL IT IS SMALL ENOUGHT TO PASS THROUGH SAID OPENING WHEREUPON SAID PLUNGER IS MOVED FORWARD BY SAID SPRING TO AN ADVANCED POSITION. 